Coverings or dressings applied to the surface of human or animal tissues can be used to protect tissue injuries, to deliver pharmaceutical or therapeutical agents and to promote wound healing. In the case of conventional therapy for most surgical and trauma wounds, including burns, one stage of treatment requires a semi-permanent covering or dressing. The purposes of this dressing can include mechanical protection of the wound, prevention of microbial contamination, prevention of wound dehydration, removal of wound exudate, and delivery of high local levels of a therapeutic agent. As wound treatments vary depending on the type and severity of the wound, several natural and/or synthetic dressings have been developed for short and long-term application. However, most of these dressings have one or more disadvantages including the need for frequent removal, difficulty in adhesion, improper mechanical properties, or difficulty in application.
Most currently available topical therapeutic formulations used with dressings are inefficient. This inefficiency results because of loss of the therapeutic agents through perspiration and mechanical action, inability of the agent to penetrate skin and mucous membranes, and crystallization or precipitation of the agents at the tissue site. Some topical therapeutic formulations are incorporated into the materials forming the dressings to be applied as patches, preformed sheets or by spray. More typically, wound coverings or dressings are used with ointments of a topical antibiotic and/or antifungal formulations. Whether used with or without dressings, topical formulations in the form of creams, ointments or liquids are difficult to apply and maintain at the injury site. They are rapidly removed by mechanical action and/or body fluid dissolution. If used in combination with a dressing, therapeutic formulations have several other drawbacks including lack of biodegradability, damage or irritation to the skin during removal of the dressing, covalent bonding or other interaction of the therapeutic agent and the dressing, inability to use a wide variety of therapeutic agents, and inadequate adhesion of the dressing.
Therefore, it is an object of the present invention to provide for a film covering or dressing for biological tissue. Another object is to provide for spray delivery of a liquid composition containing a biodegradable or bioerodible polymer which will convert to the film covering. Another object is to provide an apparatus for the spray delivery. Another object is to provide for the formation of a film dressing which is biodegradable and does not require removal from the surface of tissue while still maintaining good adhesive qualities. Another object is to provide for the formation of a film which is a semi-permeable barrier to oxygen and water while providing mechanical protection to the surface of the tissue including a barrier to organisms associated with infection. A further object is to provide for formation of a film which is capable of delivery of at least one biologically-active agent over a desired period of time. Yet another object is to provide a method for promoting wound healing on a wide variety of injured tissues like skin, mucous membranes, bones and nerves.